单例模式的Java编程简单实现

快来打我* 2022-06-08 00:35 128阅读 0赞

## 一、懒汉模式 ##

具体如下：

/* Create a Singleton class */
    class Singleton {
    	public static Singleton getInstance(){
    		return instance;
    	}
    
    	private static final Singleton instance = new Singleton();
    
    	private Singleton(){ 
    		System.out.println("Singleton()");
    	}
    }
    
    public class Lazy{
    	public static void main(String args[]){
    		Singleton s1 = Singleton.getInstance();
    		Singleton s2 = Singleton.getInstance();
    		Singleton s3 = Singleton.getInstance();
    	}
    }

## 二、饿汉模式 ##

方法1、使用同步方法，线程安全，效率低

/**
      *		getInstance() with synchronized
      */
    
    class Singleton {
    
    	public static synchronized Singleton getInstance(){
    		if(null == instance)
    		{
    			instance = new Singleton();
    		}
    		return instance;
    	}
    
    	private static Singleton instance = null;
    
    	private Singleton(){
    		System.out.println("Singleton()");
    	}
    }
    
    public class Hungry {
    	public static void main(String args[]){
    		Singleton s1 = Singleton.getInstance();
    		Singleton s2 = Singleton.getInstance();
    		Singleton s3 = Singleton.getInstance();
    	}
    }

方法2、使用同步代码块，线程安全，效率高

/**
      *		getInstance() inner content with synchronized
      */
    
    class Singleton {
    
    	public static Singleton getInstance(){
    		if (null == instance){
    			synchronized(Singleton.class){
    				if (null == instance){
    					instance = new Singleton();
    				}
    			}
    		}
    		return instance;
    	}
    
    	private static Singleton instance = null;
    
    	private Singleton(){
    		System.out.println("Singleton()");
    	}
    }
    
    public class Hungry2 {
    	public static void main(String args[]){
    		Singleton s1 = Singleton.getInstance();
    		Singleton s2 = Singleton.getInstance();
    		Singleton s3 = Singleton.getInstance();
    	}
    }

方法3、静态内部类，没有性能损耗

/**
      *		inner static class with synchronized
      */
    
    class Singleton {
    
    	public static final Singleton getInstance(){
    		return SingletonHolder.instance;
    	}
    
    	private Singleton(){
    		System.out.println("Singleton()");
    	}
    
    	private static class SingletonHolder {
    		private static final Singleton instance = new Singleton();
    	}
    }
    
    public class Hungry3 {
    	public static void main(String args[]){
    		Singleton s1 = Singleton.getInstance();
    		Singleton s2 = Singleton.getInstance();
    		Singleton s3 = Singleton.getInstance();
    	}
    }

请参考该文章，有详细讲解， [http://blog.csdn.net/jason0539/article/details/23297037/][http_blog.csdn.net_jason0539_article_details_23297037]

[http_blog.csdn.net_jason0539_article_details_23297037]: http://blog.csdn.net/jason0539/article/details/23297037/